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U.S. Geological Survey
Professional Paper 1635

The Effect of Selected Cleaning Techniques on Berkshire Lee Marble: A Scientific Study at Philadelphia City Hall

By Victor G. Mossotti, A. Raouf Eldeeb, Terry L. Fries, and Mary Jane Coombs,
U.S. Geological Survey;

Virginia N. Naudé,
Norton Art Conservation, Inc.;

Lisa Soderberg,
Vitetta Group;

George Wheeler,
Metropolitan Museum of Art, New York


photograph of statue of an armored knight with beard and lion-head hood Statue of a knight on the east façade of Philadelphia City Hall.


This publication is an online-only version of a CD–ROM publication: U.S. Geological Survey Professional Paper 1635. This publication documents virtually every part of the scientific investigation of cleaning techniques at Philadelphia City Hall. In addition to including the unabridged scientific report on the project, this publication provides field and laboratory photographs, computer programs for image analysis, and original laboratory data.


This report describes a scientific investigation of the effects of eight different cleaning techniques on the Berkshire Lee marble component of the façade of the East Center Pavilion at Philadelphia City Hall; the study was commissioned by the city of Philadelphia. The eight cleaning techniques evaluated in this study were power wash (proprietary gel detergent followed by water rinse under pressure), misting (treatment with potable, nebulized water for 24-36 hours), gommage (proprietary Thomann-Hanry low-pressure, air-driven, small-particle, dry abrasion), combination (gommage followed by misting), Armax (sodium bicarbonate delivered under pressure in a water wash), JOS (dolomite powder delivered in a low-pressure, rotary-vortex water wash), laser (thermal ablation), and dry ice (powdered-dry-ice abrasion delivered under pressure).

In our study approximately 160 cores were removed from the building for laboratory analysis. We developed a computer program to analyze scanning-electron-micrograph images for the microscale surface roughness and other morphologic parameters of the stone surface, including the near-surface fracture density of the stone. An analysis of more than 1,100 samples cut from the cores provided a statistical basis for crafting the essential elements of a reduced-form, mixed-kinetics conceptual model that represents the deterioration of calcareous stone in terms of self-organized soiling and erosion patterns. This model, in turn, provided a basis for identifying the variables that are affected by the cleaning techniques and for evaluating the extent to which such variables influence the stability of the stone. The model recognizes three classes of variables that may influence the soiling load on the stone, including such exogenous environmental variables as airborne moisture, pollutant concentrations, and local aerodynamics, and such endogenous stone variables as surface chemistry and microstructure (fracturing, roughness, and so on).

This study showed that morphologic variables on the mesoscale to macroscale are not generally affected by the choice of a cleaning technique. The long-term soiling pattern on the building is independent of the cleaning technique applied. This study also showed that soluble salts do not play a significant role in the deterioration of Berkshire Lee marble. Although salts were evident in cracks and fissures of the heavily soiled stone, such salts did not penetrate the surface to a depth of more than a few hundred micrometers. The criteria used to differentiate the cleaning techniques were ultimately based on the ability of each technique to remove soiling without altering the texture of the stone surface. This study identified both the gommage and JOS techniques as appropriate for cleaning ashlar surfaces and the combination technique as appropriate for cleaning highly carved surfaces at the entablatures, cornices, and column capitals.

Files available for downloading:

Download ReadMe text file from the CD–ROM version of this publication (20 kb).

Download Professional Paper 1635 as a 167 page PDF file (50.4 MB).

Download 156 graphic figures used in this report (198 MB).

Images - Field and laboratory photographs:
             Download 155 Core-surface images (19 MB).
             Download 11 Façade images (17 MB)
             Download 149 Electromicrograph images (30 MB)

Download PROGRAMS 4 computer programs for image analysis including: EDGE.EXE, PROFILE.EXE, SEM2BIN.EXE, and SHOWPIX.EXE (400 KB).

Download TABLES of original laboratory data:
             Download 42 comma-separated value files (.csv) (170 kb).
             Download 42 Excel (.xls) files (850 kb).

The bibliographical reference for this publication is:

Mossotti, V.G., Eldeeb, A.R., Fries, T.L., Coombs, Mary Jane, Naudé, V.N., Soderberg, Lisa, and Wheeler, G.S., 2002, The effect of selected cleaning techniques on Berkshire Lee marble; a scientific study at Philadelphia City Hall: U.S. Geological Survey Professional Paper 1635 (CD–ROM).

For questions about the content of this report, contact Vic Mossotti (

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This publication consists of the online version of a CD–ROM publication that contains, in addition to the information on this Web site, CD–ROM-autoplay files for Windows, installer software for Adobe Reader, and a search index. The data for this publication total 371 MB on the CD–ROM.

The CD–ROM (ISBN 0-607-96243-7) is available for sale by writing to:

USGS Information Services, Box 25286,
Federal Center, Denver, CO 80225
telephone: 888 ASK-USGS; e-mail:

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Created: February 28, 2002 (cad)
Updated: July 16, 2007 (bwr)